Swimming Anatomy and Lower Back Injuries in Competitive Swimmers: A Narrative Review

Abstract

Context:

Competitive swimmers are at high risk of overuse musculoskeletal injuries due to their high training volumes. Spine injuries are the second most common musculoskeletal injury in swimmers and are often a result of the combination of improper technique, high loads on the spine in strokes that require hyperextension, and repetitive overuse leading to fatigue of the supporting trunk muscles. The purpose of this review is to summarize the current evidence regarding swimming biomechanics, stroke techniques, and common injuries in the lumbar spine to promote a discussion on the prevention and rehabilitation of lower back injuries in competitive swimmers.

Evidence Acquisition:

From a PUBMED/MEDLINE search, 16 articles were identified for inclusion using the search terms “swimming,” “low back” or “lumbar,” and “injury” or “injuries.”

Study Design:

Narrative review.

Level of Evidence:

Levels 4 and 5.

Results:

The trunk muscles are integral to swimming stroke biomechanics. In freestyle and backstroke, the body roll generated by the paraspinal and abdominal muscles is integral to efficient stroke mechanics by allowing synergistic movements of the upper and lower extremities. In butterfly and breaststroke, the undulating wave like motion of the dolphin kick requires dynamic engagement of the core to generate repetitive flexion and extension of the spine and is a common mechanism for hyperextension injuries. The most common lower back injuries in swimming were determined to be lumbar strain, spondylolysis and spondylolisthesis, facet joint pain, and disc disease. Most overuse swimming injuries can be treated conservatively with physical therapy and training adjustments.

Conclusion:

Managing swimmers with low back pain requires a basic knowledge of swimming technique and a focus on prevention-based care. Since most swimming injuries are secondary to overuse, it is important for providers to understand the mechanisms underlying the swimming injury, including an understanding of the biomechanics involved in swimming and the role of spine involvement in the 4 strokes that assist in stabilization and force generation in the water. Knowledge of the biomechanics involved in swimming and the significant demands placed on the spinal musculoskeletal system will aid the clinician in the diagnosis and management of injuries and assist in the development of a proper rehabilitation program aimed at correction of any abnormal swimming mechanics, treatment of pain, and future injury prevention.

Strength of Recommendations:

B. Recommendation based on limited quality or inconsistent patient-oriented evidence.

Swimming is a low-impact, endurance-based sport with participation from all ages that provides many physical health benefits. Swimming is often utilized as rehabilitation for many land-based sport injuries, including rehabilitation for injuries to the lower back. ³⁸ Competitive swimming, on the other hand, requires significant demands; athletes typically practice for 2 to 5 hours a day year-round, averaging distances between 6000 and 24,000 meters a day. This adds up to roughly 60,000 to 80,000 meters per week.^{4,12,21,35,36} In addition to pool training, most club or collegiate training programs include land-based cross-training and strength-training programs (called “dryland”) to improve performances in the pool.

Given the high training volumes, many athletes develop chronic musculoskeletal injuries that may impact their training.^30,44 Most swimming injuries are overuse injuries, particularly in the shoulder, back, and knee. ²⁶ Spine injures are the second most common area of the body injured, with the most common being the shoulder. ¹⁵ Previous research has discovered that low back pain in swimmers has an incidence rate of 37%. ²⁹ In another study, it was reported that 50% of butterfly swimmers and 47% of breaststroke swimmers reported back pain. ⁹ A different study reported that swimmers were at higher risk of presenting with trunk asymmetries, hyperkyphosis, hyperlordosis, and had increased rates of low back pain compared with age-matched, nonathlete controls. ⁴⁹ This narrative review will discuss swimming biomechanics, stroke techniques, and common injuries in the lumbar spine to promote a discussion on the prevention and rehabilitation of lower back injuries in competitive swimmers.

Methods

For the discussion on the common back injuries involved in competitive swimming, a PubMed/MEDLINE search with the keywords “swimming,” “low back” or “lumbar,” and “injury” or “injuries” was conducted. We excluded articles that described swimming as a rehabilitation technique for chronic low back pain. Articles that were included discussed low back injuries in competitive swimmers. The majority of the journal articles that were included were narrative reviews, case-control studies (Level 3 evidence), and cross-sectional studies (Level 4 evidence). There were 2 systematic reviews also included in this narrative review. This is consistent with previous studies that demonstrated a lack of primary research regarding the prevalence of lower back pain in swimming. ¹⁰ Other references were gathered through a hand search of the citations utilized by the references included in the study. A total of 16 journal articles and textbooks were included for this portion of the study. A total of 14 additional references were included to discuss breathing and stroke techniques that are important to understanding the development of low back pain in swimmers.

Swimming Biomechanics and Technique

The goal of swimming is to maximize speed and efficiency through the water by optimizing buoyancy, reducing drag, and increasing propulsive forces. Strength and stability of the trunk muscles provide the support necessary to allow swimmers to develop proper stroke techniques to maximize efficiency and speed across large training volumes.

Optimizing Buoyancy

To stay afloat and provide a base of support in the water, swimmers utilize buoyancy to their advantage. Buoyancy of the body determines not only how well a swimmer floats but also the body’s stability in the water based on the location of the center of mass compared with the center of buoyancy. ⁴⁸ In a horizontal position, the center of mass is caudal to the center of the buoyancy, causing the legs to sink. ⁴⁸ The position of the head relative to the center of mass during breathing is important to maintaining the center of mass near the surface of the water: elite swimmers adjust their center of mass by maintaining their chest at a level just below the water, which allows their hips to be closer to the surface, causing the center of mass to be located closer to the center of buoyancy (Appendix Figure A1; available in the online version of this article). ³⁷

The trunk muscles, including the core abdominal muscles and the back extensor muscles, play a crucial role in providing buoyancy and stability for swimmers in the water. Engagement of the core muscles helps swimmers achieve proper alignment with the head, hips, and legs. Activation of the back extensor muscles allows the hips to be elevated so the center of mass is near the surface of the water.

A unique challenge of swimming is the synchronization of respiration to the stroke cycle to optimize buoyancy and stroke efficiency. ²³ During swimming, respiration is synchronized with the stroke, but is also restricted by the positioning of the body (prone or supine as opposed to upright). This, in addition to the hydrostatic pressures on the thorax while swimming, increases flow resistance and causes the diaphragm to shift upward. ² This shift causes the center of buoyancy to shift cranially and requires more support from the core, trunks, and pelvic floor muscles to maintain an advantageous center of mass during the breath. Optimizing breathing and maintaining proper spinal alignment work synergistically to improve the efficiency of a swimmer’s technique.

Reducing Drag

Reducing drag is a critical concept in swimming as it allows swimmers to move through the water more efficiently and achieve faster speeds. Drag, also known as resistance, is the force that opposes the forward motion of a swimmer. Swimmers reduce drag by maintaining a streamlined body position, which involves keeping the body aligned and extended with the head in line with the spine. Trunk muscle activation allows swimmers to maintain proper body alignment to minimize the surface area that encounters water resistance by stabilizing the spine. Maintaining a streamlined position through trunk muscle activation also allows for proper swimmer technique, which is also important in reducing drag. This includes maximizing the catch and pull phase of each stroke and optimizing stroke length through coordinated motions of the upper and lower extremities.

Increasing Propulsive Forces

Increasing propulsion contributes directly to generating greater forward forces and overcoming resistance of the water through an effective arm pull, powerful leg kick, core engagement, and effective body roll. Swimming is different from land-based sports because swimmers must create their own base of support to propel themselves through the water. ²⁶ In swimmers, the base of support that allows for force generation originates from trunk stability and strength. By providing a base of support for the extremities, the trunk muscles allow the propulsive muscles to generate maximal power with the least amount of effort. For example, during the propulsive phase of the stroke, the latissimus dorsi can act on the upper extremities to push the swimmers through the water. With a lack of spine stability, this would lead to excessive lateral movements that slow the swimmer down.

In addition, the trunk muscles link the head/cervical spine, the upper extremities, and the lower extremities involved in stroke movements. ²⁶ During swimming strokes, the power generated by the upper and lower limbs is transmitted through the trunk muscles, allowing for efficient propulsion and coordinated movements. This coordinated effort of the musculoskeletal system is called the kinetic chain.

Swimming Strokes

The 4 swimming strokes are freestyle, backstroke, breaststroke, and butterfly. This section will include a comprehensive discussion of the swimming strokes and the role of the spine involved in the biomechanics of each of the swimming strokes.

Freestyle

Freestyle, also known as the frontcrawl, is the stroke with the most events and the widest range of distances (50 yards to 1 mile in the pool and up to 10 km open water races). Freestyle is the “base” stroke and is practiced for the majority of training sessions. For each stroke, there are 5 key components involved in maximizing efficiency and speed: body position, arm motion, leg motion, breathing, and body roll. In freestyle, the swimmer lies horizontally in the water in a prone position with the body extended, the head in alignment with the spine, and the hips slightly elevated to reduce drag. Freestyle is characterized by its alternating arm movements and continuous flutter kick. The arm stroke is initiated by extending 1 arm forward at the water surface, followed by a powerful pull through backwards, and a recovery above the water surface. The “flutter kick” in freestyle involves a 6-beat continuous up-and-down kick with alternating movements throughout the stroke, with force generated through the hip flexors and extensors. Breathing is done by rotating the head to the side during the arm recovery phase, which allows the swimmer to take a breath while minimizing disruption to the body’s streamlined position. The body roll of the torso in freestyle, which is a rotation along the long axis of the torso, is important for generating force for arm propulsion and allowing the upper and lower halves of the body to move synergistically (Online Appendix Figure A2). ³¹

Successful freestyle swimming requires coordination between the arm movements, leg kick, and breathing. This is guided by the initiation of the body roll by the trunk muscles: most notably, the abdominal muscles followed by the back extensor muscles. The major trunk muscles involved in swimming include the internal and external obliques, the rectus abdominus, latissimus dorsi, and paraspinal muscles. These muscles are integral to efficient stroke mechanics in freestyle by assisting with maintaining a streamlined body position and allowing the upper and lower extremities to work synergistically through the body roll rotation that takes place during freestyle swimming. The body roll in freestyle is extremely important; it has been stated that the body roll, or lack thereof, is the greatest difference between novice and elite swimmers. ³² The roll of the torso, which can be nearly 160°, produces large forces that assist with movement of the arm through the water and is a result of the efforts of the large paraspinal muscles of the trunk. ³³ The body roll created by the paraspinal and abdominal muscles provide power for force generation and reduces drag by creating a smooth movement with the shoulders and hips moving as a single unit. This allows for reduced torque forces and spinal rotation. ³² The trunk muscles are also involved in optimizing positioning, while assisting with controlled breathing so that the swimmer may breathe as close to the water as possible when they turn their heads. By breathing close to the water, the swimmer maintains the efficient streamlined position and is able to maintain the center of mass at the surface of the water and prevent the legs from sinking if the head comes up too far over the water. Over time, efficient breathing techniques may prevent strain on the cervical and lumbar spines.

Backstroke

In backstroke, swimmers are facing the ceiling in a supine position with the body similarly in an extended position and the head aligned with the spine. The head and face remain facing upward throughout the stroke. The arm movement in backstroke is also symmetric and alternating and involves a continuous cycle between the recovery phase, entry phase, and pull phase. The arm recovery for backstroke is characterized with a straight arm arc above the water and a hand entry pinky first into the water. Similar to freestyle, the backstroke body roll also involves a rotation along the long-axis of the spine that assists in propelling the body through the water while maintaining afloat right at the surface of the water by assisting with the flutter kick (Online Appendix Figure A3).

The trunk muscles in backstroke have a similar role to the freestyle stroke: the trunk is involved in maintaining an extended body position, assisting with the body rotation, providing a base of support for force propulsion, and optimizing buoyancy. There are a couple of differences, however. In backstroke, there is no need to turn the head to breathe since the face is already facing upward. The trunk muscles, particularly the lumbar extensor muscles are activated to keep the body in a position for the head to look up and slightly back, which is the ideal position. In addition, in backstroke, the flutter kick is more important in maintaining buoyancy than in freestyle due to the supine positioning on the water. ¹¹ While a 6-beat kick is not necessary in freestyle, it is required in backstroke to maintain the optimal center of mass on the surface of the water. In addition, the gluteal and hip flexor muscles, with strong core support, play a larger role in kick propulsion to stay afloat.

Butterfly

Unlike freestyle and backstroke, butterfly and breaststroke are considered “short-axis” strokes. This means that there is no side-to-side rotational body roll to assist with movement; instead, the body rolls in a wave like movement in plane with the surface of the water, and is the driving force in transitioning from the entry phase to the pull phase and to the recovery phase in the butterfly stroke. In butterfly, the swimmer lies prone in the water, facing downward. The spine and hips are aligned and the torso undulates in a wave like motion during the stroke cycle. The arm movements in butterfly are simultaneous and symmetric throughout the stroke cycle. The leg movement in butterfly is known as the “dolphin kick.” The dolphin kick starts with a downward motion of the chest and lumbar flexion into an upward movement of the chest and lumbar extension with a subsequent follow through kick downward. The wave like motion of the dolphin kick is made possible by the engagement of the core and the dynamic tension it creates between lumbar flexion and extension, which is synchronized with the arm movements (Online Appendix Figure A4). ²⁶ The undulating movement in butterfly brings the upper torso out of the water to allow the swimmer to take a breath during the recovery phase of swimming to breathe and “fly” the arms across the water without sinking.

The undulation of the torso creates a dynamic tension in the body, which is able to facilitate the transfer of energy from the arm movement to forward momentum to the powerful dolphin kick. This is made possible through the contraction of the paraspinal muscles, which initiates this undulating movement and results in an arching of the back (hyperextension), followed by flexion of the back and contraction of the abdominal muscles and pelvic floor muscles to finish off the movement of the kick. ¹⁹ The quadriceps muscle group (rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius), hip flexor group (iliopsoas, sartorius), as well as the gluteal muscle group (gluteus medius, minimus, and medius) and hamstring muscle group (biceps femoris short ang long heads, semimembranosus, and semitendinosus) are involved in the subsequent whip-like kick and help with maintaining pelvic stability in the water.

Breaststroke

Breaststroke also lacks a body roll component and requires the trunk muscles to bring the torso up over the water, but instead of finishing in an undulating kick, the breaststroker lunges out to finish with a propulsive kick. In breaststroke, the swimmers’ body is in a prone position facing downward. The arm movements in breaststroke are symmetrical and simultaneous. The pull phase consists of a circular, scooping movement of the arms to allow the torso to rise above the water to take a breath, followed by the recovery phase that is characterized by a forward lunge into the water. The leg movement in breaststroke is known as the “frog kick” or the “whip kick.” The kick begins with drawing the legs toward the body, with the feet and knees externally rotated to set up for the kick. Then, the legs are forcefully extended backward to propel the swimmer forward.

The role of the trunk in breaststroke is to allow the coordination between the arm pull, recovery, and propulsive kick in the stroke while resetting to a streamline position between each stroke. Starting from a streamlined position, the breaststroker activates the core to scoop the arms into an adducted and supinated position and extends the lumbar spine while maintaining a neutral cervical position spine to come out over the water in a “cobra” position. Following this, the swimmer flexes the lumbar spine to lunge into the water (Online Appendix Figure A5) and finishes back in a streamlined position (see section Starts and Turns). This motion utilizes many of the same trunk muscles as the butterfly wave like dolphin kick but finishes with a greater propulsive force from the whip-like frog kick that requires a coordinated effort between the hip adductors and abductors, the hamstring and quadriceps, and the ankle dorsiflexors and plantarflexors. Breaststrokers have different stroke techniques, with some swimmers adopting a more butterfly-like technique with greater body roll movements, and other swimmers (usually those with a more propulsive kick) adopting a minimal vertical movement stroke with more glide and a stronger kick.

Starts and Turns

It is important for swimmers to understand the fundamentals of starts and turns to compete competitively. Strong turning technique is particularly important during the short course (25 yards or 25 meter pool length) season due to a largely increased number of turns compared with long course (50 meters pool length). For freestyle, butterfly, and breaststroke, the race begins with the start off the block - a flat structure located above pool level at around 29 to 30 inches above the water surface. Swimmers ready their start in a compressed flexed position. At the beep, swimmers explode off the block through a synchronized activation of the kinetic chain to dive from the block into the water to start the race (Online Appendix Figure A6). The diving portion of the start requires the spine to transition from a flexed position back to an extended position before flexing their spine while entering the water. Of note, the erector spinae and abdominal support muscles are activated synergistically to assist in the swimmer’s start.

The backstroke start is a critical, unique component of the backstroke event. It involves a specific set of movements and positions that allow swimmers to generate momentum and achieve an efficient start. The swimmers starts in the water with their arms extended, chin tucked, spine flexed, and legs crouched. At the ready position, the body is pulled out of the water by flexing the arms. At the start, the swimmer launches backward with an explosive push from the legs, moving rapidly from spine flexion to extension, and throwing the arms backward into a streamline so the hands enter the water first. This motion requires a forceful transition from spine flexion into extension and requires coordination of the trunk muscles, upper extremity muscles, and the proximal lower extremity muscles.

Before emerging from the water, the swimmers maintain a streamlined position, which keeps the body in a slight extension to reduce drag and allows the swimmer to maintain faster speeds with less effort (Online Appendix Figure A7). Competitive swimmers go into this position every time they push off the wall before breaking through the surface of the water to start swimming. The erector spinae and multifidus muscle groups are responsible for creating the streamlined body position that swimmers engage in each time they push off the wall. Depending on the swimmer’s strengths and weaknesses, some swimmers may stay underwater in a streamlined position and dolphin kick longer than others. ²⁶ Typically, swimmers maintain an underwater dolphin kick underwater for longer distances in the butterfly and backstroke events. This dolphin kick motion is similar to the undulating motion discussed in the previous section on the butterfly stroke and requires strength and flexibility of the lower trunk muscles.

Flip turns (utilized with freestyle and backstroke) require a quick contraction of the abdominal muscles and lengthening of the back muscles leading to a curled-up flexion position of the spine (Online Appendix Figure A8). Once the feet are on the wall, the swimmer is on their back underwater with their hips and spine in extension, with their knees bent before pushing off the wall. From here, the kinetic chain is similar to a vertical jump with forceful concentric contraction of the plantar flexors, quadriceps, and hip extensors. ⁴⁶ Once they push off the wall, they return to the streamlined position before breaking the surface and starting their strokes. Open turns (used in butterfly and breaststroke) require touching with 2 hands on the wall, bringing 1 hand out while swimming the legs in a tucked position onto the wall before push off. This also requires a quick abdominal muscle contraction as well as strong core lateral movement to position the legs in the ideal position before push off. The gluteal muscles and the quadricep muscles are involved in positioning the pelvis in the correct position to push off, while a coordinated effort of the lower extremity muscles is involved in the process of propelling off the wall (similar to jumping). Unfortunately, swimmers may not appreciate the importance of engaging the core muscles and proper breathing while performing flip turns.

Equipment Use

Swimmers often utilize equipment such as fins, paddles, pull buoys, snorkels, and kickboards to augment their training. When used improperly or excessively, equipment may increase load and strain on the spine and alter biomechanics. Kickboard usage in particular tends to force swimmers into hyperextension of the lumbar spine, which places additional stress on the back extensor muscles and lumbar spine to maintain buoyancy in line with the water. This may lead to improper technique, fatigue, and increased injury risk. With an existing injury, equipment use that places additional forces on the spine may exacerbate the injury and prolong recovery times. On the other hand, the use of snorkels may provide improvement in technique by removing the aspect of breathing from stroke mechanics, allowing swimmers to focus on keeping the body in line.

Dryland

“Dryland” is a term used by swimmers and coaches to represent any sort of land-based cross training. For competitive swimmers, dryland is an important part of their training regimen. Typically, dryland is a combination of resistance, interval, and strength training depending on the training regimen. An effective dryland regimen can greatly improve a swimmer’s weaknesses; on the other hand, a dryland routine that is not conducted with the proper technique may place the swimmer at risk for future injuries. ²⁶ Often, based on a swimmer’s stroke or distance specialty, dryland regimens may require individualized adaptations to optimize strengths and improve weaknesses in the pool.

Common Lumbar Spine Injuries in Swimming

Due to the challenges mentioned in the above sections, swimmers are often subjected to repetitive strains on the spine as a result of having to position themselves in unusual anatomic positions to maximize force production.

Most low back pain in elite swimmers are overuse injuries that result from repetitive stress during practices or weight training outside of the pool. ¹⁸ Low back injuries in recreational or inexperienced swimmers may also be from overuse, but may also be secondary to misuse from incorrect technique. Several aspects of swimming technique may contribute to stressing the lumbar spine. Specific risk factors for spinal injury in swimmers that have been identified in the past include overuse, growth, spinal alignment abnormalities, muscular weakness, training issues, and previous or coexisting injury. ³² In addition, previous studies have demonstrated that swimmers are at higher risk of injury when transitioning to collegiate swimming, with particularly greater incidences of injury during the first semester of college. ⁴⁷

In general, low back injuries in swimming are most common amongst butterfly and breaststroke specialists. This is due to the repetitive hyperextension and flexion movements of the lower back to maintain body position during the stroke cycle that was discussed earlier in this article. This section will discuss the most common low back injuries in swimming (Table 1).

Table 1.

Common swimming lumbar spine diagnoses

Diagnosis	Mechanism	Risk Factors	Treatment
Lumbar strain	Repetitive flexion and extension Diving	Poor technique Increased volume of training Butterfly and breaststroke	Conservative - physical therapy, ice, heat, stretching, training adjustments
Spondylolysis spondylolisthesis	Pars fracture from repeated hyperextension and axial loading	Poor technique Large volume of training butterfly and breaststroke, repeated hyperextension	8-12 weeks of rest with or without bracing Physical therapy Training adjustments
Facet joint pain	Inflammation of the facet joint from repeated hyperextension	Poor technique Large volume of training, particularly butterfly	Physical therapy Training adjustments If refractory, spinal interventions such as medial branch block and radiofrequency ablation
Disc disease	Displacement or degeneration of vertebral disc from increased loading	Poor technique Training intensity, duration, and distance of all swimming strokes	Conservative - physical therapy, training adjustments

Low Back Strain

Low back strains and sprains are the most common cause of low back pain in adolescents. ¹ Low back strain is caused by an injury to the muscles of the spine and is most common in swimmers, particularly butterfly and breaststroke swimmers. ¹⁵ The undulating motion of the torso in butterfly and breaststroke, which forces the spine to repeatedly flex and extend, places the lower back at high risk for low back strain. ¹⁹ Freestyle and backstroke swimmers are less likely to experience low back strain due to hyperextension since the spine is not constantly switching between flexion and extension; however, the rotational forces involved in the body roll in freestyle and backstroke may place swimmers at risk for low back strain. In long-axis strokes such as freestyle and backstroke, the body roll that is generated through the core allows for power generation through the hips and shoulders. Mid-distance and distance swimmers utilize more power from their core and hips than sprinters.^33,34 Therefore, contralateral rotation to generate power in mid-distance and distance freestyle stroke mechanics increase low back strain that is seen less frequently in more shoulder driven stroke patterns, such as sprint freestylers.^33,34

Low back strain may also occur in training when practicing starts off the block and backstroke starts. Injuries are due to the flexion-hyperextension movement involved in the dive and push-off portion of the start. While flip turns are not a typical cause of low back strain, repetitive flip turns may worsen a low back strain injury.

Low back strains are diagnosed on clinical examination and is a diagnosis of elimination. While low back strains are a common lower back injury in swimmers, it is important to rule out other causes of low back injuries, including some of the diagnoses mentioned below. ⁴⁵

Fortunately, muscle strains are common in swimming and typically swimmers recover quickly with activity modification, correction of biomechanical inefficiencies, core stability programs, and manual therapies. ⁴⁵ Other therapeutic modalities such as ice, heat, stretching, and nonsteroidal anti-inflammatory drugs (NSAIDs) help reduce pain and inflammation during recovery.

Spondylolysis/Spondylolisthesis

Spondylolysis is a fracture through the pars interarticularis, a bony structure in the spine. ⁶ The L5 vertebrae is most commonly injured. ⁸ Spondylolisthesis refers to a bilateral pars defect that leads to an anterior translation of the involved vertebrae relative to the next caudal level. The mechanism for spondylolysis in athletes is typically repeated hyperextension, axial loading, and/or rotational motion contributing to force exerted on the lumbar pars. ⁸ The repetitive stress results in cortical defects with a failure of bony remodeling. Although all swimming strokes maintain hyperextension of the lower back to achieve the streamlined position, the hyperextension is most exaggerated in butterfly and breaststroke. ¹⁹ The repetitiveness and high intensity of these strokes load the lumbar spine and may increase the risk of developing spondylolysis and spondylolisthesis. ¹⁶ Repeated hyperflexion associated with flip turns and open turns can also increase forces exerted on the spine and impact risk for pars injuries.

Patients with spondylolysis present with insidious onset of lower back pain, particularly in hyperextension. Radicular symptoms are uncommon with low grade pars defects. However, spondylolisthesis of grade 2 or higher will often cause moderate neuroforaminal stenosis that may present with radicular features. ³⁹ With subacute pars injuries, athletes may present with transient radicular pain that rapidly improves. ²² To diagnosis swimmers with spondylolysis, plain radiography or magnetic resonance imaging (MRI) are utilized. Sometimes, an early spondylolysis may not be discovered on radiograph and, therefore, an MRI scan, or alternatively, a computed tomography scan, may be utilized for diagnosis. ²⁶

Treatment for spondylolysis is generally nonoperative. A period of rest is recommended for around 6 to 12 weeks, with or without external bracing. ³ It is important to engage in physical therapy during the rehabilitation process. Surgical management is rarely indicated apart from high-grade spondylolisthesis or failure of conservative measures. ¹⁶ For swimmers, given the mechanism of action for spondylolysis is typically hyperextension of the spine, it may be beneficial to train different strokes (freestyle or backstroke) if butterfly and breaststroke still cause pain. Correcting improper stroke technique is also important for treatment and prevention of reinjury. In addition, the removal of training equipment, such as fins, kickboards, or pull-buoys, that produce excessive hyperextension of the lumbar spine may be beneficial to recovery. ¹⁶

Facet Joint Pain

The facet joint, also known as zygapophyseal joints, are synovial joints located between the vertebrae of the spine. The facet joint is a true synovial joint, with articular cartilage lining the contact points. Facet joint pain may arise from either the joint itself, or inflammation/irritation of the nerve that innervates the joint. As with the other extension-based back injuries, facet joint pain is also more common in breaststroke and butterfly swimmers compared with freestyle and backstroke swimmers. Facet joint syndrome is commonly referred to as “butterfly back syndrome” due to the extension required to clear water for the head during the recovery portion of the butterfly stroke. ³² In addition, fin-swimming (the utilization of fins during practice) has been shown to be related to spinal abnormalities such as facet derangement in competitive swimmers, suggesting increased loads on the spinal column with certain swimming equipment. ⁴³

Symptoms of facet joint pain may vary, but typically involve extension-based pain, with a positive facet loading examination maneuver on physical examination. The pain can radiate into the buttocks or upper thigh. As with most overuse back injuries, physical therapy is the mainstay of treatment for this condition (Online Appendix Figure A9 for examples of physical therapy exercises for the spine). For athletes with facet joint pain, outcomes are also excellent with nonoperative management. ⁴⁰ Patients may benefit from facet injection and radiofrequency ablation/medial branch blocks in more severe, refractory cases.^5,28

Disc Disease (Bulging Disc, Herniated Disc, or Degenerative Disc Disease)

Disc disease is a common cause of low back pain in athletes, particularly as they age. A bulging disc refers to the displacement of the intervertebral disc that is located in between bony vertebrae, while a herniated disc refers to protrusion of the inner core of the intervertebral disc to nearby spinal structures that often presents with more severe radicular symptoms. Degenerative disc disease refers to the process by which the height of the intervertebral disc starts to fall and lose volume, which affects the dynamics of the spine, as well as the degeneration of nearby ligaments and muscles. ³¹ The consequence of a bulging or herniated disc may involve into radicular pain due to impingement or compression of neural tissues leading to referred pain in the lower extremities. In competitive swimmers, disc disease is typically not an acute injury, but rather one that develops after years of training, and may not necessarily present symptomatically.

Competitive swimmers have a significantly greater proportion of degenerative disc changes compared with control, nonathlete groups. ¹³ This is hypothesized to be due to dynamic compression of the discs during repetitive lumbar flexion and extension; 68% of elite swimmers and 29% of recreational swimmers demonstrated degenerated discs at various levels. ¹⁷ The main variable that contributed to increase rates of lumbar intervertebral disc degeneration were training intensity, duration, and distance. ¹⁷ Unlike other common swimming back injuries, there does not appear to be a correlation with the patient’s primary stroke and risk for developing degenerative disc disease. ¹⁷ The L5 to S1 levels are the most frequently involved level of injury for disc herniation and degenerative disc disease in elite swimmers compared with recreational swimmers. High-level swimmers or masters swimmers have been shown to have an increased risk of degenerative disc disease. ¹³

Swimmers with disc disease may commonly present with focal back discomfort, pain in the upper thigh or glutes, reduced hamstring flexibility, and, occasionally, radiating pain down the leg. Physical examination findings must include a neurological examination to include sensory testing, motor testing, and reflexes as well as dural tendon tests such as straight leg raise and/or positive seated slump test to identify spinal nerve root involvement and possible disc pathology. ²⁰ For diagnosis of disc disease, an MRI scan is the gold standard. ³¹ As with most overuse injuries, conservative treatment is recommended with adjustments to their training regimen, physical therapy, NSAIDs, and a gradual return-to-sport regimen. A course of physical therapy directed at mobility, strengthening, and stability of the lumbar spine and its surrounding structures may be beneficial for symptom management and future injury prevention. Generally, athletes with radiculopathy have a favorable prognosis for return to baseline activity with conservative treatment (85% by 6 months). ⁴¹ In refractory cases, epidural steroid injection may be helpful for pain from radiculopathy and disc herniation; similarly, medial branch block/radiofrequency lesioning or intra-articular facet injection may reduce facet joint pain. ²⁵ It is rare that a swimmer with a bulging disc, herniated disc, or degenerative disc disease will require surgery during their swimming career. ¹⁴

Preventing Back Injuries in Swimmers

Low back injury prevention in swimmers is a complicated topic and is likely beyond the scope of this article. However, it is important for providers to be able to identify common risk factors for low back injuries in swimmers to better direct their rehabilitation and care. In this section, we will explain the common intrinsic and extrinsic risk factors involved with swimming injuries and briefly touch on injury prevention through improving technique, core strength and posture, and dryland. More research is required on swimming “prehabilitation,” the concept that a proactive exercise program may reduce the risk of musculoskeletal overuse injuries. Please see Table 2 for a brief summary of the common risk factors for low back injuries in swimmers identified in the currently literature, which will also be expanded on in the following section.

Table 2.

Common risk factors for low back injury in swimmers

Extrinsic Risk Factors	Intrinsic Risk Factors	Ways to Improve
Sex (women more at risk)	Weak trunk muscles	Work on proper swimming technique and breathing mechanics
Stroke (butterfly more at risk)	Lack of proper body roll	Limit swimming equipment usage especially if symptomatic
Training volume	Inaccurate breathing mechanics	Strengthen areas of weakness (particularly thoracic mobility, core and back muscle strength, hip flexion, hip abduction, scapular stabilizers)
Age started swimming	Hypermobility	Work on posture to maintain core activation and prevent hyperlordosis and hyperextension of the spine
Swimming equipment		Consider postponing youth specialization

Extrinsic Risk Factors

Extrinsic risk factors involve the environment in which an athlete performs that include factors not related to the swimming stroke or associated motions (starts and turns) themselves. A recent review article identified several risk factors that predispose swimmers to back injury. ¹⁵ The risk factors included female sex, age started swimming competitively, swimming equipment, and primary stroke. ¹⁵ However, the level of certainty for these conclusions was low, due to a limited number of existing studies in the literature on the topic. Although several of these risk factors are not able to be addressed (female sex and age started swimming competitively), other risk factors can be addressed through training adjustments. For example, the usage of equipment in and out of the pool should not be used improperly or excessively. In addition, although swimmers tend to have stroke specialties; having swimmers train all 4 strokes may reduce primary stroke-specific injuries.

Intrinsic Risk Factors

Technique

Intrinsic risk factors for low back injury in swimmers refer to the shape and positioning of the major joints of the body involved in swimming. Having proper technique is extremely important when it comes to injury prevention in swimming. ¹⁸ As previously mentioned in this article, the goal of swimming is to move efficiently through the water. A key strategy to maintaining an efficient streamlined position includes staying as close to the water as possible to take a breath in strokes like freestyle and butterfly. Torsional strain can occur when the body does not roll as a whole unit during the stroke and the swimmer’s head and position are not in line. ⁴² In both freestyle and butterfly, the body remains in line more efficiently when the swimmer is not breathing. For both freestyle and butterfly, it is important to first optimize the body motion of the stroke (the body roll and the undulating dolphin kick, respectively) before increasing training load. In freestyle, the torso from the shoulders to the hips should be moving in line from side to side, which then facilitates breathing to the side when a breath is needed. During the body roll, both the core and the back extensor muscles should be working synergistically to keep the body in line. Strategies to work on the body roll include drills, practicing breath holding, and using a snorkel to remove the action of turning the head to breathe.

In butterfly, the constant hyperextension and flexion motion of the spine that creates the undulating motion of the dolphin kick will inevitably stress the lower back. Key technique points to reduce the stress on the lower back are similar to the concepts described for freestyle. The swimmer must keep their chin as close to the water as possible during the recovery/breathing portion of the stroke to reduce the extent of hyperextension. The higher their chin rises above the water, the more the lower half of the body drops underwater, and the more the swimmer will have to keep their spine in hyperextension to stay afloat. In addition, once the head is back in the water, the swimmer who took the high-rising breath will need to implement an exaggerated flexion motion to bring their feet back to kicking level and their body back in line. Therefore, it is also very important for the swimmer to have strong abdominal and back extensor muscles to keep their body position as low to the water as possible during their stroke. In butterfly more than the other strokes, it is very easy for the stroke technique to fall apart as the swimmer fatigues, so proper technique is especially important to enforce in practice with high mileage volumes. Maintaining a breathing pattern, such as breathing every other stroke as opposed to every stroke, may help reduce the load on the lumbar spine, but requires discipline and cardiovascular stamina. Swimming drills are also important to reinforce the foundation of the body motion in butterfly.

Core and Posture

In general, having a strong core is the foundation to the prevention of back injuries in swimming. While abdominal muscles become injured infrequently, having strong core muscles are important for preventing imbalances in the spine, particularly for butterfliers, breaststrokers, and for the underwater dolphin kick. If the abdominal muscles are weak, the natural curvature of the spine can become exaggerated (hyperlordosis), placing the spine into hyperextension, which can lead to excessive loading and back pain. Having weak or tight hip flexors, which is common in swimmers, may further contribute hyperextension.

Similar to the concept of creating a balance between shoulder flexibility and rotator cuff stability in preventing shoulder injuries, there is evidence that a balance between abdominal and spine muscles is important for keeping the spine from going into hyperextension or hyperlordosis on a day-to-day basis. While swimmers spend hours in the pool, they still spend most of their hours during the day on land. It is important for swimmers to be aware of their posture not only in the water but out of the water as well. Swimmers are known to have poor posture due to the prioritized development of the chest, arms, upper back, and shoulder involved in swimming over the development of the deep postural muscles of the hips and trunk, which is likely related to hypermobility. Swimmers should avoid the common rounded, forward shoulder posture that places the spine into kyphosis and hyperextension of the lower spine that places them at greater risk for low back injury. By focusing on standing or sitting up straight out of the pool, the swimmer unconsciously activates many of the abdominal, back, and hip muscles that are all involved in supporting and mobilizing the lumbar spine, which may reduce their risk of injury in the pool.

Addressing Areas of Weakness

One feature that may differentiate some swimmers from other endurance athletes is hypermobility. It is well known that swimmers tend to have hypermobile shoulders; however, hypermobility of their other joints (spine, knees, ankles) has been documented, but not well studied. ²⁷ Hypermobility of the swimmer is often beneficial to their speed in the water; for example, swimmers are often capable of efficient underwater dolphin kicks due to the increased flexibility of the spine, knees, and ankles. However, swimmer with hypermobile joints may experience relative hypomobility in other areas, placing them at risk for injury. In addition, they may lack optimal joint proprioception and kinesthetic awareness, placing them at risk for injury. Finally, the advantages of hypermobility often do not translate well on land - swimmers tend to have areas of relative weakness (hip flexion, hip abduction weakness) and stand in a postural position (hyperextended knees, forward pelvis, rounded upper back and forward head) that is natural for their flexible bodies, but may be detrimental to their joints. Just as swimmers’ hypermobile shoulders increase their risk for rotator cuff injury and impingement, it is likely that their hypermobile spines and lower extremities may similarly increase their susceptibility for overuse injuries. ²⁷ If hypermobility is a risk factor for spine injuries in swimmers, it may benefit swimmers to strengthen supporting structures of the trunk, including the hip flexors, gluteal muscles that may assist with improving proprioceptive awareness to help prevent overuse injury from excessive spine mobility. This research regarding this topic is currently lacking, however.

The purpose of dryland, as mentioned previously, is to improve strength and prevent injury in swimmers. Introduction to new strength training techniques must be done with caution, however, since previous studies have demonstrated that 38% of new injuries in collegiate freshmen swimmers are the result of strength training. ⁴⁷ However, dryland can be an effective way to address muscle imbalances that may predispose a swimmer to injury. Many swimmers with low back pain have similar patterns of relative muscle imbalances. In general, swimmers with low back pain tend to have tight hip flexors and inhibited gluteal muscles. ⁷ It is important for swimmers to utilize spinal stabilization (also known as core stability exercises) to prevent back extensor muscle atrophy, because this can create further imbalances in the trunk that may inhibit successful rehabilitation. Swimmers are also commonly known to focus significantly on lumbar spine mobility and less on thoracic spine mobility, and thus, tend to have relative stiffness and less range of motion of the thoracic spine (see Online Appendix Figure A9 for examples of thoracic mobility exercises). For swimmers, spinal stability rehabilitation training should be focused on endurance, flexibility, and mobility rather than strength. ²⁴ Please see Table 2 for a summary of the most common evidence-based risk factors for low back injury in swimmers.

Limitations

Inherent to this study are several limitations that warrant consideration. First, the limited availability of current, existing research on the topic posed a significant challenge. While we conducted an extensive review of the literature, it became apparent that a scarcity of up-to-date, comprehensive studies directly related to our research question existed. Consequently, this scarcity may have influenced the depth and breadth of our analysis, potentially impacting the comprehensiveness of our findings.

Second, it is important to acknowledge that, whereas we examined and synthesized the literature meticulously, a narrative approach to this review introduces a degree of subjectivity in the interpretation of studies. As more research on low back injuries in swimmers is conducted in the future, a systematic review of the evidence may offer a more rigorous and standardized methodology for data extraction and synthesis and potential biases.

These limitations notwithstanding, this narrative review provides a valuable synthesis of existing knowledge on low back injuries in swimmers, sheds light on current research, and highlights areas where further investigations are warranted.

Conclusion

Managing swimmers with low back pain requires a basic knowledge of swimming technique and a focus on prevention-based care. Since most swimming injuries are secondary to overuse, it is important for providers to understand the mechanisms underlying the swimming injury. Knowledge of the biomechanics involved in swimming and the significant demands placed on the spinal musculoskeletal system will aid the clinician in the diagnosis and management of injuries. Fortunately, the majority of swimming injuries may be treated conservatively and with slight adjustments to technique.

Because overuse injuries in swimmers may differ in presentation, mechanism, and management, injuries in swimmers must be addressed on an individual basis. Proper rehabilitation includes correction of any abnormal swimming mechanics, treatment of pain, and a rehabilitation program aimed at avoiding future injury. Swimmers, therapists, physicians, and coaches are encouraged to collaborate to create the best rehabilitation plan for the swimmer to stay healthy and continue to have a long and successful swimming career.